In a decorating process of an instrument panel, a console box, and the like in the related art, a water transfer printing method using a decorative film, a film insert molding method, or the like is performed. In addition, a vacuum pressure forming method in which there is a little effect of the outside air is also performed (for example, refer to Patent Literatures 1 and 2). In the vacuum pressure forming method, a workpiece to be formed can be heated and formed in a closed off space by using a vacuum forming machine provided with upper and lower chamber boxes.